Issue #117: Provide Backdrop-unique constants for identifying Backdrop version.
Issue #117: Updating Backdrop versions in newly added modules.
Issue #1913692 by mgifford: Convert Seven to HTML5.
Issue #117: Fixing tests affected by new Backdrop version constants.
Issue #117: Updating identifiers to use 'Backdrop CMS' for clarity.
Merge pull request #216 from quicksketch/117/backdrop-version

Issue #117: Identify Backdrop version and distinguish it from Drupal 8.x.
Issue #1179764 by mjohnq3, mbrett5062, tim.plunkett: Convert Bartik to HTML5.
Issue #1943142 by jessebeach: Add the main element to the list of HTML5 elements that get set to display block.
Issue #2011578 by mortendk, tlattimore, Cottser, soulston: Markup for Stark's page.html.twig + maintenance-page.html.twig.
Issue #1190206 by cosmicdreams: Convert taxonomy-term.html.twig to HTML5.
Followup: Issue #1913692 by mgifford: Convert Seven to HTML5.
Return the profile selection minimal to its hidden state.
Merge pull request #226 from jenlampton/117-installer-fix

Return the profile selection minimal to its hidden state.
Merge pull request #215 from hellomrcat/235

Issue #1913692 by mgifford: Convert Seven to HTML5.
Merge pull request #218 from jenlampton/html5-bartik

Issue #200: Backport Converting Bartik to HTML5.
Merge pull request #213 from hellomrcat/233

Issue #1190206 by cosmicdreams: Convert taxonomy-term.html.twig to HTML5.
Merge pull request #219 from jenlampton/html5-page

Issue #200: Backport Converting page.tpl.php & maintenance-page.tpl.php to HTML5.
Issue #197: Removed theme_book_title_link() use l() instead.
Merge pull request #221 from Twinmat/238a

Issue #1943142 by jessebeach: Add the main element to the list of HTML5 elements that get set to display block.
Merge pull request #229 from ronliskey/197-ron-2

Issue #197: Removed theme_book_title_link() use l() instead.